Sounds like you've resolved your issue, but I had a similar issue a while back, so I figured I'd chime in.

In my case (and I think this was even before I switched to VOIP) my router began dropping Internet connectivity seemingly randomly. Wired connections still worked, but wireless completely stopped. Resetting the router always fixed it, for a while, but a day or two later it would stop again.

At the time I had a router that was about five years old. I have a background in computer networking and couldn't come up with a diagnosis, so I figured the router was just getting worn out. I went out and bought a new "N" router, hooked it up, and two days later my connection dropped.

At that point I went looking at the actual WiFi signal (which I should have done initially, but didn't think to). I found an open source WiFi scanner and, over a couple of days, I watched what was going on. I live in a neighborhood of old houses turned apartments inhabited by young professionals--so there are tons of access points that I can see.

Both of my routers were set to pick a channel automatically. My observations showed that the new one frequently jumpped between channel 1 and channel 11, but I never saw it on any other channels. My scanner showed that most of the access points I could see were also on channels 1 and 11. I switched my router to use channel 3 exclusively (there were no other APs using that channel at the time I checked). I have not had an issue since.

I'm not sure why routers gravitate to those two channels, but if you are living in a densely populated area and the issue returns, you may just have a saturated WiFi channel.

--Jason